A clinical trial of misoprostol, an analog of PGE1 produced by G.D. Searle & Co., on treatment of duodenal ulcer was carried out in five hospitals in Beijing, Shanghai, and Guangzhou. Totally 94 cases were treated with misoprostol 200 micrograms q.i.d. for 4 weeks. A parallel comparison was made, using cimetidine 200 mg q.i.d. A double-blind, double-dummy study was conducted. The result showed that the therapeutic efficacy of misoprostol in duodenal ulcer is similar to that of cimetidine. The ulcer healing rate in four weeks being 60.7% and 67.9% respectively, while the overall effectiveness rate being 77.7% and 80.2%. There was no statistically significant difference between the two medication groups. The side effect of misoprostol is mainly mild diarrhea (6.4%), but it disappears despite the continued use of medication. To our impression, misoprostol represents a new therapeutic approach for treatment of peptic ulcer in addition to acid controlling H2 blockers.